I wouldn't say orange spotted filefish, Oxymonacanthus longirostris, are particularly rare but I've only ever seen 2; the fish below and its mate which is just out of picture.

An interesting thing about these guys is that they are obligate corallivores; meaning they can only survive by eating coral, specifically the polyps of Acropora sp. What this really means is that in spite of their gorgeousness they should not be kept in aquaria by all but the most spectacularly skilled aquarists. The failure to understand this fact has killed a lot of these beautiful fish by starvation. This one and its mate were thriving at home in Mobul, Philippines, but they are distributed around the indopacific which is, in my view the best place to see them.